SPP1 and hepatocellular carcinoma: Wang et al. found that miR-21 is enriched in serum exosomes of HCC patients which may serve as a diagnostic biomarker.38 Decreased expression of serum exosomal miR-718 was associated with recurrent HCC.39 In this study, we found that plasma exosomal S100A4 and plasma OPN levels were significantly associated with prognosis of HCC patients, and the combination of exosomal S100A4 and OPN had a better prognostic performance than each alone.